Havenít tried a vapor barrier liner in your sleep system yet? Want to sleep warmer in colder temperatures? Want to keep your downís loft high? Donít want to lug an extra pound or two or three of gross condensed sweat in your down items each day, or deal with trying to let your down items air out to dry each morning? Get a vapor barrier liner to use in your sleeping system.
I splurged and had one constructed from cuben fiber. I think Zpacks made it for me. Canít remember. Slept toasty warm last night hanging on a high mountain ridge at 28 degrees F with constant light/moderate wind. Zpacks hammock tarp with doors closed. About 18 inches of open space from ground to lower edges of tarp. 20 degree down bag pulled peapod style over/around hammock (Grand Trunk Nano7). Smartwool long sleeve shirt and longjohn pants. Vapor barrier liner. Tucked a Montbel extra light down sweater on top of the vapor barrier toward the head opening of the bag, to seal out any draft. Fleece beanie.
Slept so warm I think I might have been able to have used my 40 degree bag instead of my 20 degree bag. In the morning, I could feel that my smartwool top and bottoms were pretty moist with condensed sweat vapor, and the vapor barrier liner was pretty moist. I turned the VBL inside out while packing up my campsite, and it dried in minutes. This cuben VBL compresses down to about half the diameter of a tennis ball.
If that amount of moisture had made it into my down bag, I would have been stuck carrying that weight with me after breaking camp and the loft would have decreased somewhat.
I have considered what sounds like a potentially equivalent system that would be way less expensive than my cuben VBL. I would think that a tight-fitting, super cheapo disposable pair of rain pants like you can buy in the dollar store, made of cheap, thin, light-weight, non-breathable plastic, paired with a cheap 02 rain jacket or driducks rain jacket, would accomplish the same thing as my cuben VBL, and the jacket would serve double duty during the daytime if a rain shower appeared. Iím guessing that the breathable quality of the 02 jackets or driducks jackets really isnít all that effective and the jacket probably traps 90 percent of sweat vapor. Not sure.
Anyway, if you havenít tried a VBL in colder camping, I highly recommend that you consider it.